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• Description

  Sodium thiosulfate is a commonly used chemical material, as the fixing agent in photography, film and printing plate-making industry, as a reducing agent used in tanning. It is used as a bleaching agent for removing residual and a mordant in the paper and textile industries, as antidotes of cyanide poisoning in medicine, as dechlorination agent and fungicides of drinking water and wastewater in water treatment, as a copper corrosion inhibitor of circulating cooling water and a deoxidizer of boiler water systems. It is also used for Cyanide wastewater treatment. Soda ash and sulfur are generally used as raw materials in industry, soda ash reacts with sulfur dioxide produced by the combustion of sulfur to produce sodium sulfite, then add sulfur for boiling reactions, and then filter, bleach, concentrate and crystallize, etc, can obtain sodium thiosulfate pentahydrate. Other production waste containing sodium sulfide, sodium sulfite, sulfur and sodium hydroxide can also be used, after appropriate treatment to get the product.
  
  The above information is edited by Yan Yanyong of Chemicalbook. ;

• Physical properties

  Sodium thiosulfate has two forms as anhydrous sodium thiosulfate (Na2S2O3) and sodium thiosulfate pentahydrate (Na2S2O3 · 5H2O), the latter is also known as soda and Hyperion. A molecular weight is 158.11 and 248.18 respectively. Anhydrous sodium thiosulfate is an opaque crystalline powder. The relative density is 1.667. It is odorless, salty taste, soluble in water, insoluble in ethanol. It decomposes in acidic solution, has a strong reduction, easily absorbs moisture. Sodium thiosulfate pentahydrate is odorless, colorless and transparent monoclinic crystals or granules. The relative density is 1.685. The melting point is 48 ℃. It loses all crystal water at 100 ℃, and decomposes above 100 ℃. It is easily weathered in dry and hot air, slightly deliquescence in the hot and humid air. It is soluble in water and turpentine, insoluble in ethanol, decomposes in case of strong acid. Prolonged exposure in the air, it is easily oxidated and carbonized by oxygen and carbon dioxide. ;

• Chemical Properties

  It is colorless monoclinic crystal or white crystalline powder, Odorless, salty ignorant. The relative density is 1.667. Soluble in water, the solubility is 231 g/100 ml of water at 100 ℃. Insoluble in alcohol. deliquescence easily in air. With a strong reductibility, decomposition in acidic solution. ;

• Reactions

  With reductibility, sodium thiosulfate is a medium strength reducing agent, for example, can be oxidated by chlorine:
  Na2S2O3 + 4Cl2 + 5H2O = Na2SO4 + H2SO4 + 8HCl
  this reaction is used in textile and paper industries, and sodium thiosulfate is used as dechlorination agent. Again, it can be oxidized to sodium tetrathionate by iodine:
  Na2S2O3 + I2 = Na2S4O6 + 2Nal
  this reaction is used in analytical chemistry for quantitative determination of iodine.
  It is also used in tanning, extracts silver from the ore and so on. Since there are different oxidation states of sulfur in sodium thiosulfate molecule, it is stable in alkaline medium, unstable an acidic medium, oxidation-reduction reaction occurs when acidification, separate out sulfur:
  Na2S2O3 + H2SO4 = Na2SO4 + H2S2O3 H2S2O3 = H2SO3 + S H2SO3 = H2O + S02.
  With coordination, thiosulfate ions can form stable complexes with certain metal ions, for example, silver bromide can be dissolved in an aqueous solution of hypo to produce stable [Ag (S2O3) 2] 3-complex ions:
  AgBr + 2Na2S2O3 = Na3 [Ag (S2O3) 2] + NaBr, so it is commonly used as a photographic fixing bath. Sodium sulfite and sulfur are boiled, and then filtration, evaporation, crystallization to prepare sodium thiosulfate. ;

• Uses

  1. Sodium thiosulfate is Used in manufacture of the fixing powder and preparation of the photographic industry fixer, desiccant. Used as a reducing agent of dichromate in leather tanning industry.
  2. Sodium thiosulfate is an important inorganic chemical raw material. It can be used in the synthesis of pesticides Bisultap, Thiosultap disodium, CARTAP and so on.
  3. Used as analytical reagents, mordant and fixer.
  4. Used as new insecticides, with stomach poisoning, uptake and contact action effects, it can prevent and treat rice yellow stem borer, stem borer, leaf roller, rice thrips and vegetables, fruit pests.
  5. With uptake and strong contact, stomach poisoning effects, it can prevent and treat various rice pests and vegetables, fruit pests.
  6. Used as the chlorine removal agent for Pulp and cotton fabric bleached, as chelating agents, anti-oxidants in the food industry, as detergents, disinfectants in the pharmaceutical industry.
  7. Used as chelating agents, antioxidants, anti-browning agent, as the dechlorination agent of chlortetracycline hydrochloride (or chlortetracycline) chilled with ice, dechlorination reaction is as follows:
  More chlorine content will cause side reactions of free sulfur, so only used for very dilute concentrations of chlorine.
  Used as salt chelating agent, limited content is 0.1% or less. ;

• Preparation

  Sodium thiosulphate is an important chemical commodity that is known to photographers as "hypo". It can be prepared by the reaction of sodium sulphite and the bisulphite with H2S:
  2Na2S03 + 2NaHS03 + 2H2S -> 3Na2S203 + 3H20
  It can also be prepared by the reaction of sulphur with sodium sulphite above 60 °C
  Na2SO3 + S -> Na2S2O3 and by the reaction of H2S and permanganate.
  Sodium thiosulphate decomposes at 310°C to form sulphur and Na2S03 , and at 400°C to form Na2S4 and Na2S. It absorbs S02 to form free sulphur and Na2S04 . Sodium thiosulphate forms many hydrates and their solubility relationships are quite complex.

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• Production method

  1. It is generated by heat of a solution of sodium sulfite and sulfur powder.
  2. There are more synthesis methods of sodium thiosulfate, such as sodium sulfite method, sodium sulfide method and so on.
  Sodium sulfite method
  Soda solution reacts with sulfur dioxide gas, and caustic soda was added, adding sodium sulfide to remove impurities by filtration, and then sulfur powder was dissolved in a hot solution of sodium sulfite to react, filter, remove impurities, and then filter repeatedly, add caustic alkali to process, through concentration, filtration, crystallization, centrifugal dewatering, screening, to obtain the finished product of sodium thiosulfate. Reaction equation: Na2CO3 + SO2 = Na2SO3 + CO2 ↑
  Na2SO3 + S + 5H2O = Na2S2O3 · 5H20
  Sodium sulfide method
  A raw material liquid formulated from sodium sulfide evaporation residue, barium sulfide wastewater (containing sodium carbonate and sodium sulfide) reacts with sulfur dioxide, sulfur powder was added after clarification, heated to react, evaporation, cooling crystallization, washing, separation, screening to obtain sulfur thiosulfate products. Reaction equation: 2Na2S + Na2CO3 + 4SO2 = 3Na2S2O3 + CO2 ↑
  2Na2S + 3Na2CO3 + 6SO2 + 2S = 5Na2S2O3 + 3CO2 ↑
  3. Dehydration method is that heat sodium thiosulfate pentahydrate crystalline indirect with steam, it dissolves into itself crystal water, concentration, centrifugal dewatering, drying, screening, to obtain the finished product of anhydrous sodium thiosulfate.
  Na2S2O3 · 5H20 → Na2S2O3 + 5H2O ;

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